Folding chairs are relatively popular, because they can be stored with considerably reduced space requirements when compared to non-folding chairs. Nevertheless, folding chairs still require relatively large space, since the dimension of the folding chair is generally reduced only along one space coordinate (e.g., reduced length). To further reduce the space requirement, collapsible chairs have been developed, in which further size reduction is achieved by folding the chair along at least two space coordinates (e.g., length and width). Various collapsing chairs are known in the art.
For example, Cook et al. describes in U.S. Pat. No. 5,921,621 a collapsible chair with a foldable backrest, in which the chair has four legs that support the corners of a flexible square seat. The legs are movably attached to each other at about their respective midpoints, and the seat is collapsed in width and depth by turning the legs around the midpoint. While Cooks chair is relatively easy to unfold and collapse, Cooks chair provides relatively little stability and is prone to tipping over.
Improved stability can be achieved by including slidable cross bars between the legs as described in U.S. Pat. No. 6,082,813 to Chen and U.S. Pat. No. 5,984,406 to Lee. Chen's chair advantageously collapses to a relatively compact form. However, the position of the back support is limited to a vertical position, which may not be comfortable over a prolonged period. On the other hand, Lee's chair provides an angled backrest, although it lacks a seat support entirely.
In addition to the problems of the collapsible chairs mentioned above, all or almost all of the known collapsible chairs suffer from a common disadvantage in that the seat will loose tension once the seat supports the weight of a person. Moreover, where known chairs are collapsible in a single motion, such chairs do typically fail to provide a seat support rod onto which the seat can be tensioned. Alternatively, where known chairs have a pair of seat support rods, such chairs generally require at least two folding motions (e.g., one motion in which the seat is folded upwards followed by one motion in which the seat is folded in a side-to-side movement). Therefore, there is a need to provide improved methods and apparatus for collapsible chairs.